In November 2003 the WMO/GAW Regional Brewer Calibration Centre for Europe (WMO RA-VI region) (RBCC-E) was established at Izaña Observatory (IZO). The project is also intended to contribute to the GAW Programme in the RA-VI Region as a part of the closer co-operation between WMO and the European Commission being stated in the Memorandum of Understanding signed by WMO and EC in December 2003.
The RBCC-E reference is based on three double Mark-III Brewer spectroradiometers (the IZO triad): a Regional Primary Reference (B157), a Regional Secondary Reference (B185) and a Regional Travelling Reference (B183). The IZO triad is regularly sun-calibrated by means of Langley method and by external lamps. The travelling reference ensures reference transference to the WMO-Region VI Brewer network.
The Izaña’s RBCC-E’s reference triad (Brewers #157, #183 and # 185)
Though B157, B183 and B185 are routinely calibrated by Langley plots method, these absolute calibrations are not used for definition of a new calibration scale. The Meteorological Service of Canada (MSC) triad is respected as the official reference of the GAW Brewer international scale. The establishment of the IZO triad allows the implementation of a self-sufficient European Brewer calibration system that respects the world scale but works as independent GAW infrastructure. The IZO triad is linked to the world reference MSC triad with yearly calibrations towards the Canadian travelling reference B017. Systematic extraterrestrial constants (ETC) have been obtained by Langley method with B157 from 1998 to 2007. A comparison against ETCs transferred by travelling B017 shows an agreement within 1% in this period.
The function of RBCC-E also allows development and testing of new measurement techniques for the ground Brewer network like zenith, polarimetric, UV or aerosol optical depth measurements at IZO. A radiation laboratory and an electronic workshop are available at IZO for accurate fittings and indoors calibration and maintenance of the triad instruments.